Need more help figuring out fork length for new (used) frame

I was originally planning on converting my '94 Stumpjumper to a rigid SS, but I got frustrated trying to find parts for a frame that has a 1" HT. I ended up buying a used Giant XTC2 frame and build it up, but I'm having issues figuring out how long of a fork I need.

Let me know if my math is correct. According to Giant, this frame originally came with a 100mm RockShox Dart 3 fork. That fork is listed as having a 471mm axle to crown length, but if I back out 25% sag, that drops the A2C down to 446mm. Does that sound like about the right length I need to find?

I've seen forks ranging from 435mm up to 450mm. What do you think would be the right length so that I don't change the bike's geometry significantly?